The invention disclosed herein relates generally to facilitating electronic communications. More particularly, the present invention relates to systems and method for allowing a plurality of IP telephony devices to communicate with each other without requiring the use of a telephony gateway or similar call set up service.
Many modern corporate telecommunications systems implement what is referred to as a private branch exchange or PBX. An organization implements a PBX system, typically comprising various hardware and software components, to switch calls between organization users on a series of internal lines, each terminating at the PBX. The PBX switches calls between these internal users over the local lines, thereby eliminating the need for calls to connect over external lines to a switch on the Public Switched Telephone Network (PSTN), e.g., over a plurality of locals loops connected to a switch that the Local Exchange Carrier (LEC) maintains.
The PBX, in addition to connecting users within an organization over a plurality of local lines, is connected to a LEC via one or more external lines. Most modem digital PBX systems utilize software to multiplex a number of calls from internal users to destinations outside the organization over significantly fewer external lines. For example, one or two digital Ti lines may provide sufficient bandwidth to carry the voice and data traffic for an organization of several hundred employees. Organizations realize significant financial gains from using the PBX through elimination of the need to maintain a line for each user in the organization to the telephone company's central office.
In IP telephony networks that provide Voice over IP (VoIP) communications, an IP telephony gateway is attached to the organization's PBX system. The gateway is also attached to an IP network over which it communicates with IP telephony devices, such as an IP telephone handset. The gateway receives the voice data (which may or may not be digitized), significantly compresses it, encodes the data as 1P packets for transport over the network and routes it to a destination, e.g., another IP telephony device on the gateway's local network or to the PBX to transport over the public switched telephone network (PSTN). The gateway also provides translation between communication protocols or formats, as well as call setup and cleanup on both its LAN and switched circuit interfaces.
Because IP telephony devices are typically “dumb” devices, they are unable to send or receive calls to or from PBX based telephone or telephones otherwise connected to the PSTN without the presence of a gateway on the LAN to which the IP telephony device connects. Moreover, the IP telephony devices will not be able to communicate with other IP telephony devices on the local network as the telephony gateway provides address resolution functionality, e.g., between a SIP URL and IP address. Thus, systems and methods are required that that provide PBX functionality on an IP telephony network, e.g., routing calls between local IP telephony devices, in the event that a network's gateway or similar call setup service fails.